1. Field of the Invention
The present invention relates to a gas turbine installation for providing torque by combustion gas that is produced by burning compressed air together with fuel. More particularly, the present invention relates to a gas turbine installation having an exhaust plenum downstream of a turbine, to a cooling air supplying method for use in the gas turbine installation, to a method of modifying a gas turbine installation.
2. Description of the Related Art
In a turbine section of a gas turbine, turbine cooled vanes exposed to the highest temperature and most of other components must be cooled. For example, an exhaust diffuser of a double tube structure is generally connected to a combustion gas outlet of a turbine for the purpose of restoring the static pressure of mainstream gas. An exhaust plenum including such an exhaust diffuser is also one of the components to be cooled. The exhaust plenum usually comprises inner and outer exhaust diffusers, inner and outer exhaust casings disposed so as to cover those exhaust diffusers, a strut for coupling the inner and outer exhaust casings to each other, a strut cover for coupling the inner and outer exhaust diffusers to each other in a covering relation to the strut, and so on. The exhaust plenum thus constructed is generally cooled by a method of supplying, as a coolant, compressed air exhausted from a compressor to a space between the outer exhaust casing and the outer exhaust diffuser, and then introducing the compressed air to a space between the inner exhaust casing and the inner exhaust diffuser through a space between the strut and the strut cover (see, e.g., Patent Reference 1: JP,A 2001-182503).